1. Field of the Invention
The present invention relates to a method of manufacturing a rotary shaft integral with a hard faced journal, more particularly to a method of manufacturing a rotary shaft such as an auger shaft adapted for use in an auger type icemaker.
2. Description of the Prior Art
In manufacture of a rotary shaft such as an auger shaft in an auger type icemaker, a layer of antiabrasive and anticorrosive alloy is formed on a cylindrical surface of a journal base metal of the rotary shaft by build-up spraying to enhance resistance of the journal against abrasion and corrosion. The alloy layer formed by built up spraying is, however, apt to be separated from the base metal of the journal due to its thinness and shallow penetration into the base metal, particularly if the fuse process after build up spraying is insufficient. To overcome this problem, it has been proposed to form a layer of antiabrasive and anticorrosive alloy on a cylindrical surface of the base metal of the journal by build up welding or hard facing. Although in the process of build up welding or hard facing, the alloy layer is formed thick on the base metal and deeply penetrates into the base metal, there will occur cracks in the alloy layer if preheat of a portion of the base metal to be welded is insufficient.
For the purpose of avoiding such a problem as described above, it has been proposed to prepare a pair of journal base metals separately from a body portion of the rotary shaft thereby to form a layer of the alloy on each cylindrical surface of the journal base metals by build-up welding or hard facing. In this case, the journal base metals are coaxially connected at their one ends to opposite ends of the body portion of the rotary shaft by friction welding. In such a manufacturing process as described above, however, there will occur cracks in the welded or hard faced alloy layer unless the journal base metals are sufficiently preheated before the process of build-up welding or hard facing.